In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in an LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band, which ranges from 1.4 MHz to 20 MHz. Also, in the UMTS network, successor systems of the LTE system (referred to as, for example, “LTE-Advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) are under study for the purpose of achieving further broadbandization and increased speed.
In radio communication, as uplink (UL) and downlink (DL) duplexing methods, there are frequency division duplexing (FDD), which divides between the uplink and the downlink based on frequency, and time division duplexing (TDD), which divides between the uplink and the downlink based on time. In the event of TDD, the same frequency is applied to uplink and downlink transmission, so that the uplink and the downlink are divided based on time and transmitted from one transmitting point. Since the same frequency is used between the uplink and the downlink, a transmitting point (radio base station) and a user terminal both have to switch between transmission and reception alternately.
Also, in TDD in the LTE system, frame configurations (transmission ratios between uplink subframes and downlink subframes (DL/UL configurations)) to support a plurality of different types of asymmetrical uplink/downlink resource allocation are defined (see FIG. 1). In the LTE system, as shown in FIG. 1, seven frame configurations, namely DL/UL configurations 0 to 6, are defined, where subframes #0 and #5 are allocated to the downlink and subframe #2 is allocated to the uplink. Also, to prevent interference between transmitting points (or between cells), the same DL/UL configuration is applied between neighboring transmitting points.